全文获取类型
收费全文 | 27208篇 |
免费 | 1782篇 |
国内免费 | 1729篇 |
出版年
2023年 | 479篇 |
2022年 | 475篇 |
2021年 | 801篇 |
2020年 | 728篇 |
2019年 | 1096篇 |
2018年 | 1003篇 |
2017年 | 673篇 |
2016年 | 698篇 |
2015年 | 846篇 |
2014年 | 1758篇 |
2013年 | 2009篇 |
2012年 | 1184篇 |
2011年 | 1603篇 |
2010年 | 1274篇 |
2009年 | 1366篇 |
2008年 | 1377篇 |
2007年 | 1414篇 |
2006年 | 1229篇 |
2005年 | 1106篇 |
2004年 | 944篇 |
2003年 | 768篇 |
2002年 | 682篇 |
2001年 | 511篇 |
2000年 | 470篇 |
1999年 | 475篇 |
1998年 | 387篇 |
1997年 | 385篇 |
1996年 | 342篇 |
1995年 | 350篇 |
1994年 | 321篇 |
1993年 | 281篇 |
1992年 | 275篇 |
1991年 | 258篇 |
1990年 | 206篇 |
1989年 | 203篇 |
1988年 | 169篇 |
1987年 | 166篇 |
1986年 | 116篇 |
1985年 | 249篇 |
1984年 | 294篇 |
1983年 | 220篇 |
1982年 | 237篇 |
1981年 | 224篇 |
1980年 | 214篇 |
1979年 | 163篇 |
1978年 | 132篇 |
1977年 | 125篇 |
1976年 | 146篇 |
1975年 | 89篇 |
1974年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
91.
Enzymic Synthesis of Leukotriene B4 in Guinea Pig Brain 总被引:9,自引:8,他引:1
Takao Shimizu Yutaka Takusagawa Takashi Izumi Nobuya Ohishi Yousuke Seyama 《Journal of neurochemistry》1987,48(5):1541-1546
Leukotriene B4 [5(S), 12(R)-dihydroxy-6, 14-cis-8,10-trans-eicosatetraenoic acid] was obtained from endogenous arachidonic acid when slices of the guinea pig brain cortex were incubated with the calcium ionophore A 23187. Enzymes involved in its synthesis, arachidonate 5-lipoxygenase [arachidonic acid to 5(S)-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid and subsequently to leukotriene A4] and leukotriene A4 hydrolase (leukotriene A4 to B4), were present in the cytosol fraction. Arachidonate 5-lipoxygenase was Ca2+-dependent, and was stimulated by ATP and the microsomal membrane, as was noted for the enzyme from mast cells. The lipid hydroperoxides stimulated 5-lipoxygenase by four- to sixfold. The leukotriene A4 hydrolase activity was rich in brain, and the specific activity (0.4 nmol/min/mg of protein) was much the same as that of guinea pig leukocytes. High activities of these enzymes were detected in the olfactory bulb, pituitary gland, hypothalamus, and cerebral cortex. Since leukotriene B4 is enzymically synthesized in the brain, possible roles related to neuronal functions or dysfunctions deserve to be examined. 相似文献
92.
Pertussis Toxin Attenuates D2 Inhibition and Enhances D1 Stimulation of Adenylate Cyclase by Dopamine in Rat Striatum 总被引:2,自引:1,他引:1
The response of adenylate cyclase to GTP and to dopamine (DA) was investigated in synaptic plasma membranes isolated from rat striatum injected with pertussis toxin, which inactivates the inhibitory guanine nucleotide-binding regulatory protein (Ni) of adenylate cyclase. Pertussis toxin treatment reverted the inhibitory effects on the enzyme activity elicited by micromolar concentrations of GTP and reduced by 50% the DA inhibition of cyclase activity via D2 receptors. The toxin treatment enhanced the net stimulation of enzyme activity by DA in the presence of micromolar concentrations of GTP. However, the stimulatory effect of the selective D1 receptor agonist SKF 38393 was not significantly affected. The data indicate that Ni mediates D2 inhibition of striatal adenylate cyclase and participates in the modulation of D1 stimulation of the enzyme activity by DA. 相似文献
93.
Effect of Digestion with Phospholipase A2 on Endogenous Protein Phosphorylation in Particulate Fractions from Rat Brain Synaptosomes 总被引:1,自引:1,他引:0
The endogenous phosphorylation of synapsin 1 in cyclic AMP-containing media was greatly decreased by digestion of synaptic vesicles and synaptosomal membranes with phospholipase A2, suggesting that the system is functionally dependent on the membrane structure. Treatment of the synaptic vesicle fraction with phospholipase A2 also caused a small but significant inhibition of the Ca2+/calmodulin-dependent phosphorylation of the same protein. The Ca2+/calmodulin-dependent phosphorylation of other major acceptors, and the basal phosphorylation of a 52-kD acceptor enriched in the vesicle fraction, remained unchanged after cleavage of the membrane phospholipids with phospholipase A2. The significance of the selective effect of phospholipase A2 treatment on endogenous membrane phosphorylation is discussed. 相似文献
94.
95.
用淀粉凝胶电泳,分析苹果实生苗新梢皮层的过氧化物酶同工酶,其酶9带(A_9)与苹果的矮生习性相关,且不受树龄、苹果类型以及栽培条件等影响。在矮生型苹果育种中,A_9可以作为预选标志,其准确率为86.14%。 相似文献
96.
Types I and IV collagenolytic and plasminogen activator activities in preovulatory ovarian follicles 总被引:1,自引:0,他引:1
A Palotie T Salo K K Vihko L Peltonen H Rajaniemi 《Journal of cellular biochemistry》1987,34(2):101-112
During ovulation, enzymatic degradation of the extracellular matrix occurs within and around the graafian follicles. In this study, the activities of several different proteolytic enzymes were measured in the culture media of follicles taken from pregnant mare serum gonadotropin (PMSG)-primed immature rats. At 52 h after PMSG, the follicles were cultured for 2 to 15 h in media with or without human chorionic gonadotropin (hCG). Type I collagenase activity in hCG-stimulated follicles gradually increased within 6 h to 3.3-fold above that of the controls. Relatively pure populations of granulosa cells produced type I collagenase to a similar extent. Likewise, type IV collagenase increased 3.8-fold by 6 h after exposure of the follicles to hCG. In contrast, plasminogen activator activity increased by 3.9-fold at 2 h after hCG, but was negligible at 4, 6, and 15 h after incubation. These results suggest that plasminogen activator may activate both type I and type IV collagenase in hCG-stimulated ovulatory follicles. 相似文献
97.
Effect on aflatoxin production of competition between wild-type and mutant strains of Aspergillus parasiticus 总被引:4,自引:0,他引:4
K. Ehrlich 《Mycopathologia》1987,97(2):93-96
Co-cultivation of a strain of Aspergillus parasiticus, capable of making aflatoxins, with blocked mutant strains, capable of producing none or only a low level of aflatoxins, reduced the net yield of aflatoxins more than that expected based on spore recovery. Yields of aflatoxins were 8-fold less for a norsolorinic acid-producing strain, 14-fold less for an averantin-producing strain, 6-fold less for an averufin-producing strain, and 21-fold less for a versicolorin A-producing strain when co-cultured in equal amounts with a wild-type strain of Aspergillus parasiticus. Even when the wild-type strain was initially present in 100-fold excess, with two of the mutant strains, reduced aflatoxin production was still observed. 相似文献
98.
Effect of roasting on ochratoxin A level in green coffee beans inoculated with Aspergillus ochraceus
Haruo Tsubouchi Katsuhiko Yamamoto Kazuo Hisada Yoshio Sakabe Shun- ichi Udagawa 《Mycopathologia》1987,97(2):111-115
The heat stability of ochratoxin A in green coffee beans inoculated with Aspergillus ochraceus was studied. Heat treatment (roasting) at 200 °C for 10 or 20 min reduced the levels of ochratoxin A by only 0–12% in the dried whole beans. Almost all of the ochratoxin A was infused into the coffee decoction when the roasted samples were ground and extracted with boiling water. Therefore, the reduction of ochratoxin A concentration of contaminated coffee beans by roasting under these conditions is ineffective. 相似文献
99.
Bertil Löwkvist Hadar Emanuelsson Lo Persson Frank Sundler Anders Lundquist Dr. Olle Heby 《Cell and tissue research》1987,247(1):75-84
Summary The localization of ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis and thus in cell growth, was determined in the 4.5-day-old chick embryo, using two independent methods of analysis. ODC protein was identified by indirect immunofluorescence with a monospecific ODC antibody, and catalytically active ODC was identified by autoradiography with -(5-3H) difluoromethylornithine. Both methods revealed a basically similar distribution of ODC within the embryo. Among the organs, the brain exhibited the highest ODC levels. ODC levels were also high in spinal cord, mesonephric tubules and heart. Similar levels, but confined to limited areas, were found in liver tissue, head mesenchyme, and the oral and pharyngeal regions. Organs that exhibited high ODC levels are all engaged in rapid growth, as well as in extensive tissue remodeling and differentiation. 相似文献
100.
Summary Distribution, localization and fine structure of the stellate cells in the liver of lamprey, Lampetra japonica, were studied during the spawning migration by use of Kupffer's gold-chloride method, fluorescence microscopy for vitamin A (retinol) and electron microscopy. The stellate cells in the lamprey liver differ in some of their properties from those in mammalian livers. Stellate cells which store abundant retinol in lipid droplets, occur not only in the hepatic parenchyma, but also in the dense perivascular and capsular connective tissue of the liver and in the interstitium of pancreatic tissue. In the hepatic parenchyma these cells are located perisinusoidally or along thick bundles of collagen fibrils. The stellate cells display a number of large retinol-containing lipid droplets, granular endoplasmic reticulum, tubular structures, dense bodies, Golgi complex, microtubules, and microfilaments. In the space of Disse, the stellate cells and extracellular fibrilar components such as collagen fibrils and microfibrils (11–12 nm in diameter) are intervened between the two layers of basal laminae. Differentiation and possible functions of the stellate cells in the lamprey liver are discussed. 相似文献